Process for producing hexafluoroacetone or its hydrate

ABSTRACT

Hexafluoroacetone or its hydrate is produced in a higher yield than that of the conventional process (1) by oxidizing a heptafluoroisobutenyl ether with ozone or (2) by thermally decomposing an octafluoroisobutyl ether or a heptafluoroisobutenyl ether in the presence of oxygen and an activated carbon catalyst.

This is a continuation of application Ser. No. 189,034, filed May 2,1988, now U.S. Pat. No. 4,885,398, and the benefits of 35 USC 120 areclaimed relative to it.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for producing hexafluoroacetone orits hydrate, and more particularly to a process for producinghexafluoroacetone or its hydrate with effective utilization ofoctafluoroisobutene or its adduct with alcohol etc.

2. Description of the Prior Art

Hexafluroacetone is a monomer for producing a synthetic resin, asynthetic rubber, etc., or is used as an intermediate for crosslinkingagents such as bisphenol AF, etc., or as an intermediate raw materialfor medicaments, agricultural chemicals, etc.

The following processes have been so far proposed for producinghexafluoroacetone or its hydrate having the said applications. ##STR1##

However, the foregoing processes have the following disadvantages.

(1) Oxidation reaction by potassium permanganate proceeds vigorously andthe by-produced manganese dioxide is an industrial waste which is hardto treat.

(2) High purity oxide is hard to synthesize from hexafluoropropene andthus the produced hexafluoroacetone contains hexafluoropropene, etc.

(3) In the oxidation of hexafluorothioacetone dimer by nitric acid, theproduced hexafluoroacetone hydrate contains NO₂ and SO₂, whose removedis troublesome.

(4) In the use of hexachloroacetone, chlorine not only contributes toincrease the weight, but also is synthetically not efficient, andfurthermore toxic antimony pentachloride is required. Thus, a highpurity product is hard to obtain.

Besides the foregoing prior art, a process for producinghexafluoroacetone or its hydrate by reaction of heptafluoroisobutenylalkyl ether with oxygen under light irradiation has been proposed by thepresent Applicant [Japanese Patent Application Kokai (Laid-open) No.61-277,645], but the yield on the basis of raw materialheptafluoroisobutenyl alkyl ether is as low level as 19.2 to 19.4%.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a process for producinghexafluoroacetone or its hydrate more advantageously than theconventional process based on oxidation by potassium permanganate,by-producing manganese dioxide or the process based on oxidation byexpensive periodic acid.

Another object of the present invention is to effectively utilizeoctafluoroisobutene or its adduct with alcohol etc.

Further object of the present invention is to improve the yield ofhexafluoroacetone or its hydrate when produced from octafluoroisobutylether or heptafluoroisobutenyl ether as a raw material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

These objects of the present invention can be attained by producinghexafluoroacetone or its hydrate according to one of the followingprocesses:

(1) a process for oxidizing a heptafluoroisobutenyl alkyl, aryl orbenzyl ether with ozone,

(2) a process for thermally decomposing an octafluoroisobutyl loweralkyl, phenyl or benzyl ether at a temperature of 50° to 600° C. in thepresence of oxygen and an activated carbon catalyst, and

(3) a process for thermally decomposing a heptafluoroisobutenyl loweralkyl, phenyl or benzyl ether at a temperature of 50° to 600° C. in thepresence of oxygen and an activated carbon catalyst.

Octafluoroisobutene as the starting material is a byproduct from theproduction of hexafluoropropane as one of the important raw materialsfor fluorine-containing copolymers. Generally, this highly toxicoctafluoroisobutene is readily capable of forming octafluoroisobutylalkyl ethers as alcohol adducts with lower alcohols, such as methanol,ethanol, n-propanol, isopropanol, n-butanol, etc. Likewise, aryl ethersor benzyl ether are formed as adducts of phenols or adduct of benzylalcohol.

The octafluoroisobutyl ethers are dehydrofluorated with a hydroxide orcarbonate of an alkali metal or alkaline earth metal or a base such as atrialkylamine with stirring in the presence of an interphase transfercatalyst such as a quaternary ammonium salt, etc., whereby thecorresponding heptafluoroisobutenyl alkyl, aryl or benzyl ether can beobtained.

According to the process (1), oxidation of the heptafluoroisobutenylalkyl, aryl or benzyl ether with ozone is carried out. In the oxidationwith ozone, heptafluoroisobutenyl alkyl, aryl or benzyl ether is chargedinto a glass reactor vessel, and bubbled with an ozone-containing oxygenor air by an ozone generator of silent discharge type in the absence ofa solvent or in the presence of a solvent such as hydrocarbon,halogenated hydrocarbon, ether, water or the like with vigorousstirring.

In the oxidation, hexafluoroacetone (HFA) or its hydrate seems to besynthesized through an ozonide compound, as given by the followingequations: ##STR2## where R is an alkyl group of C₁ to C₁₀, aryl groupor benzyl group.

The ozone is used in the oxidation at a concentration of about 2.5 toabout 400 mg per l of oxygen or air and in a molar ratio of about 1 tothe heptafluoroisobutenyl alkyl, aryl or benzyl ether. The oxidationtemperature is usually -70° to 110° C., preferably -40° to 60° C.

After the oxidation, the reaction mixture is usually successively led toa water trap and a dry ice-methanol trap to recover the product. Fromthe water trap, hexafluoroacetone is obtained as a hydrate. The thusobtained hydrate itself of hexafluoroacetone can be used as a solventfor polyester, polyamide, etc., and can be also dehydrated withphosphorus pentoxide, concentrated sulfuric acid, sulfuric anhydride, ormolecular sieves [Japanese Patent Applications Kokai (Laid-open) Nos.57-81,433 and 59-157,045].

Formation of hexafluoroacetone in the decomposition gas obtained by theoxidation with ozone can be defected by GLS analysis, but owing to theexistence of other by-product gases in the decomposition gas, thedecomposition gas is once introduced into water to make and separate thehydrate of hexafluoroacetone without direct separation ofhexafluoroacetone. This procedure is very simple and convenient.

The oxidation with ozone has a yield of 22.5% on the basis ofheptafluoroisobutenyl alkyl ether and a yield of 69.7% on the basis ofthe introduced ozone. The former yield is considerably better than thatobtained by oxidation with oxygen under the irradiation of ultravioletrays as disclosed in said Japanese Patent Application Kokai (Laid-open)No. 61-277,645.

In said processes (2) and (3), either octafluoroisobutyl ether orheptafluoroisobutenyl ether derived therefrom can be used as the rawmaterial, whereas in the process previously proposed by the Applicant,that is, the process for producing hexafluoroacetone or its hydrate byreaction of heptafluoroisobutenyl ether with oxygen under theirradiation of light [Japanese Patent Application Kokai (Laid-open) No.61-277,645], only heptafluoroisobutenyl ether can be used as the rawmaterial and octafluoroisobutenyl ether cannot be used as the rawmaterial.

Thermal decomposition reaction of these raw materials can be carried outby passing the raw mateial together with oxygen or an oxygen-containinggas in a molar ratio of the oxygen to the raw material of about 1 toabout 2 through a metallic reactor tube filled with an activated carboncatalyst under the atmospheric pressure or a superatmospheric pressure.

The activated carbon for use as the catalyst can be in any shape such asa powdery form, a granular form, a pellet form, a honeycomb form, a barform, a cylindrical form, etc., and particularly it is desirable to usean activated carbon catalyst in a granular form having a specificsurface area of about 1 to about 300 m² /g, preferably about 20 to about200 m² /g.

The reaction in the presence of such an activated carbon catalyst iscarried out at a temperature of about 50° to about 600° C., preferablyabout 150° to about 300° C. Below about 50° C., the thermaldecomposition rate is too low and a lower temperature is not preferablefrom the pointview of economy and efficiency, whereas above about 600°C. the energy cost is increased and the deterioration of the reactormaterial is accelerated, and thus a higher temperature is notpreferable.

Recovery and dehydration of hexafluoroacetone hydrate after theoxidation can be carried out in the same manner as in the process (1).

The oxidation in the presence of such an activated carbon catalyst has ayield of about 29 to about 30% on the basis of the raw material, whichis higher than obtained in the process (1).

PREFERRED EMBODIMENTS OF THE INVENTION

The present invention will be described in detail below, referring toExamples.

EXAMPLE 1

200 g (0.88 moles) of heptafluoroisobutenyl methyl ether (purity: 93%)was charged into a flask having a capacity of 300 ml, provided with aDimroth condenser, a stirrer and a gas inlet, and about 504 l ofozone-containing oxygen at an ozone concentration of 27.1 mg/l wasbubbled into the charged heptafluoroisobutenyl methyl ether at thetemperature of 25° C. with vigorous stirring for 16.8 hours. The off-gaswas introduced into 1.5 l of water in another flask and further into 500ml of dry ice-methanol trap, and then discharged.

About 2.5% by weight of hexafluoroacetone hydrate was formed in thewater trap (1459 g), as determined according to the F-NMR internalstandard method, and extracted and separated with an etheral solvent.From the reactor flask and the dry ice-methanol trap, 30.5 g and 134.2 gof the raw material were recovered, respectively.

Yield based on the raw material: ##EQU1##

Yield based on the introduced ozone: ##EQU2##

EXAMPLE 2

A stainless steel reactor tube filled with 110 g of calcined activatedcarbon was heated to the temperature of 200° C., and 150 g (0.45 moles)of octafluoroisobutyl methyl ether (purity: 70%) was passed through thereactor tube from the overhead together with 11 l (0.49 moles) of anoxygen gas for 1.6 hours. The gas leaving the reactor tube wasintroduced into 100 ml of water in a flask having a capacity of 300 mland further into a dry ice-methanol trap having a capacity of 500 ml anddischarged.

In the water trap (content: 129.2 g), hexafluoroacetone hydrate (HFA·H₂O) was formed at a concentration of about 18.9% by weight, as determinedaccording to the F-NMR internal standard method, and likewise 2.95 g ofan aqueous layer containing hexafluoroacetone hydrate at a concentrationof about 18% by weight was also formed in the dry ice-methanol trap.Besides the aqueous layers, 45.7 g of the raw material was recovered.Separation of the hexafluoroacetone hydrate from the aqueous layers wasreadily carried out by extraction with an etheral solvent.

Yield based on the raw material: ##EQU3##

Yield based on the oxygen: ##EQU4##

EXAMPLE 3

Thermal decomposition was carried out in the same manner as in Example2, except that 150 g (0.61 mole) of heptafluoroisobutenyl methyl ether(purity: 87%) was used in place of the octofluoroisobutyl methyl etherand passed through the reactor tube together with 16.4 l (0.73 moles) ofan oxygen gas for 2 hours.

After the reaction, hexafluoroacetone hydrate was formed at aconcentration about 22.9% by weight in the water trap (content: 121.1 g)and 19.6 g of an aqueous layer containing hexafluoroacetone hydrate at aconcentration of about 23% by weight was also formed in the dryice-methanol trap. Besides the aqueous layers, 14.3 g of the rawmaterial was recovered.

Yield based on the raw material: ##EQU5##

Yield based on the oxygen: ##EQU6##

EXAMPLE 4

Thermal decomposition was carried out in the same manner as in Example2, except that 150 g (0.44 moles) of heptafluoroisobutenyl benzyl ether(purity: 85%) was used in place of the heptafluoroisobutyl methyl etherand passed through the reactor tube together with 11.9 l (0.53 moles) ofan oxygen gas for 1.7 hours.

After the reaction, hexafluoroacetone hydrate was formed at aconcentration of about 18.5% by weight in the water trap (content: 128.0g) and 2.1 g of an aqueous layer containing hexafluoroacetone hydrate ata concentration of about 19% by weight was formed in the dryice-methanol trap. Besides the aqueous layers, 58.6 g of the rawmaterial was recovered.

Yield based on the raw material: ##EQU7##

Yield based on the oxygen:

What is claimed:
 1. A process for producing hexafluoroacetone or itshydrate, which comprises thermally decomposing an octafluoroisobutyllower alkyl, phenyl or benzyl ether in the presence of oxygen and anactivated carbon catalyst at a temperature of 50° to 600° C.
 2. Aprocess according to claim 1, wherein the thermal decomposition iscarried out by passing the octafluoroisobutyl ether through a metallicreactor tube filled with the activeted carbon catalyst together withoxygen or an oxygen-containing gas.
 3. A process according to claim 2,wherein the octafluoroisobutyl ether and the oxygen or anoxygen-containing gas are passed through the reactor tube in a molarratio of the oxygen to the octafluoroisobutyl ether of 1 to
 2. 4. Aprocess for producing hexafluoroacetone or its hydrate, which comprisesthermally decomposing a heptafluoroisobutenyl lower alkyl, phenyl orbenzyl ether at a temperature of 50° to 600° C. in the presence ofoxygen and an activated carbon catalyst.
 5. A process according to claim4, wherein the thermal decomposition is carried out by passing theheptafluroisobutenyl ether through a metallic reactor tube filled withthe activeted carbon catalyst together with oxygen or anoxygen-containing gas.
 6. A process according to claim 5, wherein theheptafluroisobutenyl ether and the oxygen or an oxygen-containing gasare passed through the reactor tube in a molar ratio of the oxygen tothe heptafluoroisobutenyl ether of 1 to 2.